Implantable medical devices, such as pacemakers, defibrillators and cardioverters (collectively referred to as implantable cardiac stimulating devices) are designed to monitor and stimulate the heart of a patient that suffers from a cardiac arrhythmia. Using leads connected to a patient's heart, these devices typically stimulate the cardiac muscles by delivering electrical pulses in response to measured cardiac events which are indicative of a cardiac arrhythmia. Properly administered therapeutic electrical pulses often successfully reestablish or maintain the heart's regular rhythm.
Implantable cardiac stimulation devices (hereinafter "implantable stimulation devices") can treat a wide range of cardiac arrhythmias by using a series of adjustable parameters to alter the energy, shape, location, and frequency of the therapeutic pulses. The adjustable parameters are usually defined in a computer program stored in a memory of the implantable stimulation device. The program (which is responsible for the operation of the implantable device) can be defined or altered telemetrically by a medical practitioner using an implantable device programmer. Modern implantable stimulation devices have a great number of adjustable parameters that must be tailored to a particular patient's therapeutic needs. In addition, implantable stimulation devices also have a significant number of diagnostic parameters that, when retrieved from an implantable stimulation device by the medical practitioner using the implantable device programmer, inform the medical practitioner about the operational characteristics of the implantable stimulation device and the device components.
One diagnostic parameter of particular importance in an implantable stimulation device is the recommended replacement time of the device. Electrical energy necessary to maintain proper operation of an implantable stimulation device is provided by a battery connected to energy-consuming components of the device such as a pulse generator, the memory, and control circuitry. The battery differs from other implantable stimulation device components in that other device components are typically designed to last indefinitely, while available energy of the battery is consumed during its normal use. Eventually, output voltage of the battery falls to a level that is insufficient to operate the implantable stimulation device within limits specified by the therapeutic requirements of the device. By this time the battery is no longer useful and must therefore be replaced. Because the battery is typically built into the implantable device casing, replacement of the battery requires a surgical procedure to replace the implanted device with a new device equipped with a fully charged battery.
It is highly desirable to predict this failure of the battery well in advance so that arrangements may be made for replacement of the implantable stimulation device in which the battery is at or approaching very low capacity. Thus, the concept of a recommended replacement time for implantable stimulation devices has been developed to provide ample warning to a medical practitioner that a particular device with a battery reaching dangerously low capacity may need to be replaced in the near future.
To implement this concept, most modern implantable stimulation devices incorporate battery diagnostic circuitry that monitors the condition and operational characteristics of the battery. A recommended replacement time indicator, defined as a diagnostic parameter and stored in the device memory, is set by the device to an active state when the battery diagnostic circuitry determines that the battery has reached its recommended replacement time.
After initial implantation and configuration of the implantable stimulation device, the medical practitioner typically performs periodic follow-up examinations to determine whether the therapy delivered by the device is having the desired effect and the device is otherwise operating properly. In particular, it is of utmost importance to determine whether the recommended replacement time indicator has been set to the active state so that the medical practitioner may plan for possible device replacement.
However, the recommended replacement time indicator may be accidentally set to the active state even though the battery has not yet reached its recommended replacement time. This may occur for a number of reasons--for example, the indicator may be set to the active state due to high output pacing by the device, by externally delivered defibrillation, or by defibrillation delivered by an implantable defibrillator. As a result, the active recommended replacement time indicator may erroneously indicate that the implantable stimulation device needs to be replaced--a highly undesirable situation.
It would thus be desirable to provide a system and method for assisting the medical practitioner in verifying whether an active recommended replacement time indicator has been properly set by the implantable stimulation device. It would further be desirable to enable the medical practitioner to change an improperly set recommended replacement time indicator to an inactive state.